This invention relates in general to the field of orthopedic spinal surgery. In particular, this invention relates to an improved device for correcting a spinal deformity such as scoliosis and to an improved unidirectional rotatory pedicle screw that can be used in such a spinal deformity correcting device. This invention is particularly well suited for correcting spinal deformities in growing children and adolescents.
Scoliosis is a common spinal deformity that frequently occurs in growing children and adolescents. The majority of patients who develop scoliosis do not have any underlying skeletal disorder at birth, but develop spinal deformity during adolescence. Since there is no defined and obvious cause for development of scoliosis in this age group, it is usually called idiopathic scoliosis. Most patients with adolescent idiopathic or juvenile scoliosis are treated with conventional bracing until maturity or until the undesired curve deteriorates to such a significant degree that surgical correction is warranted. Several external, developmental, and radiological markers (such as family history, age at menarche, Risser sign, Tanner staging, severity of curve at presentation, documented progression, and chronologic age) are utilized to predict the severity and potential for progression of a curve. Oftentimes, it becomes difficult to accurately predict if a scoliosis deformity will become worse over time. Therefore, patients with curves of over twenty-five degrees and having the associated risk factors are typically braced until skeletal maturity.
Several genetic markers are being developed that have the potential to accurately predict which patients will eventually develop a significant deformity that would necessitate surgery. Those patients who are genetically not predisposed to progression of a mild scoliosis may simply be observed without expensive and cumbersome bracing. However, those patients who are genetically predisposed to significant worsening before skeletal maturity may benefit from preemptive surgery at a time when the curve is still small. Early surgery may be advantageous in children in whom genetic testing results are positive for future worsening of scoliosis deformity. Smaller curves would be amenable to improved correction and would mitigate further progression of spinal and rib deformity. Other advantages of such an approach would include less surgical trauma from minimally invasive surgery, shorter hospital stay, less bleeding and scarring, improved correction and an ability to modulate growth with a fusion-less surgical correction of deformity. Subsequent removal of hardware and ability to maintain mobility of the scoliotic segment would also be significant benefits.
Most current methods of treatment include surgical correction of curves over forty-five degrees to fifty degrees with segmental instrumentation and fusion. Occasionally, some patients develop scoliosis in their pre-teen years or may have congenital scoliosis. Such spinal deformities are occasionally temporarily stabilized by internal growing rod construct. Typically, growth may be modulated by stapling or other tether mechanisms from the anterior approach utilizing thoracoscopic techniques. However, bilateral rods or cables or a hybrid technique combining rods and cables are more commonly performed for improved correction of the deformity.
Most current posterior instrumentation systems include several anchors that are strategically placed on both sides of the spinal curve. Then, the concave side is typically elongated and convex size rod or cable is compressed. Frequent surgical procedures are necessary to alter the construct to accommodate spinal growth and to correct any spinal deformity that may have developed since previous surgery. It would, therefore, be advantageous to have a minimally invasive spinal fixation system that addresses above-mentioned concerns associated with some of the current methods of treatment of adolescent idiopathic scoliosis.